1. Field of the Invention
This invention relates to a zoom lens apparatus for use, for example, with a video camera.
2. Description of the Prior Art
A zoom lens apparatus, for example, for use with a video camera or the like is conventionally constructed such that a lens barrel in which a lens system including a zoom lens, a focusing lens and an iris all disposed on a single optic axis is accommodated, a zoom lens driving section for driving the zoom lens, a focusing lens driving section for driving the focusing lens and an iris driving section for driving the iris to open or close are constructed in an integrated relationship with each other.
An exemplary one of such conventional zoom lens apparatus is shown in FIG. 19. Referring to FIG. 19, the zoom lens apparatus shown in generally denoted at a and includes a lens barrel b holding a plurality of lenses thereon and having a substantially cylindrical shape, and a lens driving mechanism c disposed at an upper portion of an outer peripheral face of a rear portion of the lens barrel b.
A cylindrical focusing lens ring d which serves also as a focusing lens barrel is formed from part of the lens barrel b, and a focusing lens e is held on the inner side of an end portion of the focusing lens ring d. The focusing lens ring d is screwed to an end portion of a zoom lens barrel h which will be hereinafter described such that, when the focusing lens d is turned, it is moved in a forward or rearward direction with respect to the other lens barrel b thereby to move the focusing lens e in a direction of an optic axis thereof.
Meanwhile, a toothed portion or gear f is formed over a range of almost 180 degrees in a circumferential direction at a substantially mid portion in the forward and rearward direction of an outer peripheral face of the focusing lens ring d, and an output gear of a focusing lens driving section which will be hereinafter described is held in meshing engagement with the toothed portion f.
A zoom lens ring g is outwardly fitted for turning motion on a zoom lens barrel h which is part of the lens barrel b, and if the zoom lens ring g is turned, then a zoom lens (not shown) supported for movement in the forward and rearward direction on the inner side of the zoom lens barrel h is moved in the direction of its optic axis so that the focal length of the lens system is varied.
The zoom lens ring g has an outer diameter substantially equal to the diameter of the focusing lens ring d, and a toothed portion or gear i is formed over a range of about 180 degrees in a circumferential direction on an outer peripheral face of a rear end of the zoom lens ring g. An output gear of a zoom lens driving section which will be hereinafter described is held in meshing engagement with the toothed portion i.
A rear half portion j of the lens barrel b except the focusing lens ring d and the zoom lens barrel h has an outer diameter substantially equal to two thirds of an outer diameter of the focusing lens ring d and the zoom lens ring g, and has a flange portion k formed at a front end portion thereof such that it projects outwardly. The lens driving mechanism c is disposed on the upper side of the outer peripheral face of the lens barrel b rearwardly of the flange portion k.
A focusing lens driving section l for driving the focusing lens e and a zoom lens driving section m for driving the zoom lens are included in the lens driving mechanism c, and each of them includes an individual speed reducer as hereinafter described.
A focusing motor n is disposed at a location of about 45 degrees rightwardly obliquely upwards from the center of the lens barrel b on an outer peripheral face of the rear half portion j of the lens barrel b.
A zooming motor o is disposed at a position displaced a little leftwardly from just above the center of the lens barrel b on the outer peripheral face of the rear half portion j of the lens barrel b.
A gear case p accommodates therein speed reducers q and r individually for the focusing lens driving section l and the zoom lens driving section m. The gear case p is secured to a portion of an upper portion of the outer peripheral face of the rear half portion j of the lens barrel b in the proximity of the zoom lens barrel h.
The focusing motor n and the zooming motor o are secured to a support plate s which is securely mounted at a rear end portion of the gear case p such that a suitable distance may be provided between the support plate s and the gear case p.
A drive shaft t projects forwardly from the gear case p, and a pinion u is secured to a front end of the drive shaft t. The pinion u is held in meshing engagement with the toothed portion f of the focusing lens ring d, and the drive shaft t is rotated by the focusing motor n by way of the speed reducer q provided in the gear case p.
Another drive shaft v projects forwardly from the gear case p, and a pinion w is secured to a front end of the drive shaft v. The pinion w is held in meshing engagement with the toothed portion i of the zoom lens ring g, and the drive shaft v is rotated by the zooming motor o by way of the speed reducer r provided in the gear case p.
Thus, when the motor n of the focusing lens driving section l rotates, the focusing lens d is rotated to perform focusing, and when the motor o of the zooming lens driving section m rotates, the zoom lens ring g is rotated to perform zooming.
It is to be noted that also an iris driving section for driving an iris to open and close not shown is provided in the zoom lens apparatus a.
With the conventional zoom lens apparatus a described above, since the focusing lens driving section l, the zoom lens driving section m and so forth, which are composed of the motors n and o, the gears provided in the gear case p and so forth, are mounted in a condition wherein they project outwardly from the lens barrel b, the zoom lens apparatus a has a complicated outer profile with convexes and concaves and is bulky. Consequently, the zoom lens apparatus a is low in efficiency in storage, transportation and so forth. Besides, not only the profile of an appliance such as a video camera in which such zoom lens apparatus a is adopted is increased in size and it is difficult to handle, but also there are problems that operation sounds of the motor n and o, the gear wheels and so forth leak to the outside and are offensive to the ear of a user of the video camera and that such operation sounds are, upon photographing using the video camera, recorded.